Abnormal sleep duration and cardiovascular disease

Although the mechanisms are not clear, both short and long sleep have been associated with increased risk of cardiovascular disease.

Epidemiology

Epidemiologic studies have consistently found a U-shaped association of sleep duration with mortality and morbidity attributed to both cardiovascular and noncardiovascular causes. Both short sleep (i.e., 6 hr) and long sleep (>8 hr) have been associated with coronary heart disease, stroke, diabetes, hypertension, and hypercholesterolemia (25).

Pathophysiology

There are several potential mechanisms by which short sleep could elicit cardiovascular disease. Some evidence suggests that short-term sleep curtailment can increase sympathetic nervous system activity, increase blood pressure, and impair glucose tolerance.

In contrast with the risks of short sleep, the potential risks associated with long sleep have been scarcely addressed. One plausible mechanism by which long sleep could contribute to cardiovascular disease is via arousals from sleep. It has been shown that long sleepers have more fragmented sleep than average or short-duration sleepers (25). Both spontaneous and experimentally induced arousals from sleep are associated with surges in sympathetic nerve activity, cortisol, and blood pressure (25).

Treatment of Abnormal Sleep Duration

A host of treatment strategies are available to increase sleep duration. Simple sleep hygiene instructions, included in table 27.1, can be helpful (18). Sleeping pills are not recommended for chronic (>4 weeks) treatment because of associations of chronic use with mortality, tolerance, and rebound insomnia with discontinuance. Cognitive behavioral therapy is preferred for chronic management of poor sleep.

One of the most effective behavioral treatments for insomnia is sleep restriction treatment. Insomnia is often perpetuated or exacerbated by spending excessive time in bed in an effort to compensate for disturbed sleep. Having an insomniac spend less time in bed can result in consolidated and refreshing sleep. Clinicians have generally not addressed how to treat abnormally long sleep duration, which has not been regarded as harmful. Nonetheless, sleep restriction therapy would be an obvious treatment to consider (25).

Exercise for Short and Long Sleep

In epidemiologic studies, low levels of exercise have been one of the most robust correlates of both short and long sleep (25). A causal link between these variables could operate in either direction. Low levels of exercise could impair sleep or make one feel less energetic, resulting in long sleep. On the other hand, there is evidence suggesting that both short and long sleep may cause a person to become less active. Thus, epidemiologic studies of sleep duration and mortality and morbidity rates, which have typically controlled for exercise, might have underestimated the risks of long and short sleep. Short sleep could lead to fatigue, which is a significant predictor of low activity. Short-term sleep extension studies as well as anecdotal accounts indicate that spending extra time in bed leads to feelings of lethargy, which could also make one less willing or able to engage in physical activity. Chronically, extra time in bed could also be hazardous because this would involve >=1 hr of more of completely sedentary behavior and would allow less wakefulness time to engage in physical activity.

Exercise is a particularly attractive alternative or adjuvant sleep treatment for multiple reasons. First, epidemiologic studies have consistently shown that exercise is associated with better sleep. Second, exercise has been endorsed by most sleep experts as a means of improving sleep. Third, exercise would be far healthier than pharmacologic treatment and conceivably simpler and less expensive than traditional cognitive behavioral treatment.

Most of the literature on exercise and sleep has been restricted to normal sleepers and thus is probably limited by ceiling and floor efforts (i.e., there is little room for improvement in sleep quality). Nonetheless, significant (albeit modest) improvement in sleep has been found in this population. Larger effects of exercise have been noted in people with insomnia, but this information has been limited primarily to self-report data.